There are at least five known and current processes for forming CMCs using ceramic cloth. Those processes generally include: 1) prepregging, wherein ceramic cloth is run over a series of rollers and through tensioners, dipped into a slurry tank, dried in a tower, sandwiched between layers of plastic sheeting, and rolled onto a tube; 2) chemical vapor infiltration, wherein a preform of ceramic cloth plies is set inside a chemical vapor reactor, the preform is heated, and atoms or molecules in the form of vapor are deposited on and, hopefully, within the ceramic cloth; 3) lanxide process, wherein a special chemical is processed into ceramic cloth, and the ceramic cloth is dipped into a liquid metal bath that converts the special chemicals to ceramic materials; 4) melt infiltration, wherein the ceramic cloth preform is infiltrated with a liquid metal; after which the infiltrated preform is processed to convert the metal to a ceramic; and 5) slurry infiltration, wherein a ceramic particle containing slurry is vacuum infiltrated into the ceramic cloth preform, and the ceramic cloth preform is then heat treated to form the CMC.
Slurry infiltration processes are preferred when abrasion and other damage to the ceramic cloth fibers is a concern, and where complete infiltration of the cloth with a liquid ceramic precursor is desired. The problem with the slurry infiltration process is that it may require multiple infiltration/heat treatments to form a proper CMC. The number of infiltration/heat treatments is dependent upon the yield of ceramic material from the ceramic slurry. Additionally, known slurry infiltration methods yield incomplete infiltration of the tow bundle within the woven ceramic cloth. Another problem is that fiber damage results from mechanical handling of the ceramic cloth and during known slurry infiltration processes, especially in processes that use cleaned or desized ceramic cloths. Desizing is a cleaning process that removes the sizing on the fiber, and is performed prior to any infiltration. Incomplete tow bundle infiltration results in low strength areas in the CMC because there is insufficient matrix between the fibers to transfer load. Fiber damage in the ceramic cloth during infiltration is almost inherent in any process that requires rollers and tensioning devices due to the action of the fibers rolling over one another. The rolling action causes nicks in the fibers that result in CMC strength reduction. All of these problems yield CMCs with reduced structural properties and reliability.
Therefore, what is needed is a method of slurry infiltration that minimizes damage to the ceramic cloth, and that maximizes slurry infiltration of the tow bundles and fibers of the cloth.